Earth Science Chapter 8 Section 1 Mass Movements Earth Science Chapter 8 Section 1

Mass Movements Landforms change through processes involving Wind Water Ice Gravity Down slope movement of soil and weathered rock from the force of gravity is called Mass Movement

Mass Movement Climate has an effect on weathering in certain areas Climatic conditions determine the extent of mass movement Mass movement can Be barely detectable Sudden slides, falls and flows Materials range in size from mud to boulders

Factors that influence Mass Movements Material’s weight Materials’ resistance to sliding or flowing- friction How cohesive the material is or if it is anchored to bedrock Triggers- shake the material loose Mass movements occur when the force pulling the material down slope that is stronger than the force holding it in place.

Creep Slow steady downhill flow of loose weathered material May be only a few centimeters a year Noticeable over long periods of time Solification- creep that occurs in areas of permafrost Mud-like liquid when water is released from melting permafrost Saturates the surface Unable to drain Surface area slides

Mudflows Mud flow Swiftly moving mixtures of mud and water Triggered by earthquakes or similar vibrations Common when volcanoes melt snow Water fills spaces in sediment and allows them to slide down hill Common in sloped, semi arid areas that experience intense rain fall

Lahar Type of mud flow that occurs after a volcanic eruption Melted snow mixes with ash and flows downslope

Slides Landslide Rapid downslope movement of material Thin block of soil, rock and debris separate from underlying bedrock Material slides as one block with little internal mixing Common on steep slopes after saturation

Slides Rock slide Sheet of rock moves downhill on a sliding surface Triggered by earthquakes Move a large amount of material

Slumps Material moves along a curved surface Material at the top moves downhill and slightly inward Material at the bottom moves slightly outward Occurs with thick soils on moderate to steep slopes Common after rains Can be triggered by earthquakes Leave a crescent shape scar on slope

Avalanches Occur in mountains with thick accumulation of snow Sun melts surface which refreezes at night- icy crust Snow falls on this crust and builds up Becomes heavy and slides down slope Triggers Vibrations as slight as a single skier

Rock Falls Rocks are loosened by physical weathering processes Rocks break loose and fall directly downward They bounce and roll Produce a cone shaped pile of coarse debris at the base of the slope- called a talus Common at high elevations in steep cut roads and rocky shorelines Less likely in humid regions- rocks are covered with soil

Mass Movements Affect People Mass movements are natural processes, however humans can contribute Construction of buildings and roads- make slopes unstable Poor maintenance of septic systems- leaks

Reducing the Risk Catastrophic mass movements occur on slopes greater than 25 ° that experience annual rainfall of 90 cm Risk can be reduced by Digging trenches to divert water Not building at the base of a slope Covering steep slopes with nets Contructing fences along highways where movement is common Prevention measures are only temporarily successful